1. Field of the Invention
The present invention relates to a circuit board device and a design support device. More specifically, the present invention relates to a circuit board device used in electronic equipment such as information equipment, and particularly to a structure for a circuit board device that can suppress electromagnetic radiation in a circuit board in which a power supply pattern and a ground pattern are formed, and a design support device thereof.
2. Description of the Related Art
Unwanted electromagnetic radiation has become a problem in recent years in various types of information equipment. The unwanted radiation is thought to stem from signal wires, or wires connected to signal wires, that transmit clock signals on a circuit board and digital signals synchronous with the clock signals. Filtering and damping resistance have come to be used on the signals as measures to counter the unwanted radiation.
Further, it has also come to be known in recent years that unwanted radiation is generated due to instability of the electric potential at the power supply system of the circuit board, and various methods for stabilizing electric potential have been proposed. An example of such a method includes providing a bypass capacitor in the IC power supply to absorb fluctuations in electric potential arising in the power supply system.
In addition, unwanted radiation due to electrical resonance of the power supply and ground surface is also generated in circuit boards having a power supply and ground surface that span the entire board.
As a countermeasure, Japanese Patent Application Laid-Open (JP-A) No. 10-112574 discloses a technology to suppress unwanted radiation by connecting, in addition to a capacitor connected between a digital IC power supply pin and a ground surface, a capacitor between the power supply and the ground surface at a circuit board end, and suppressing at the board end resonance current reflection distributed in the surface generated by electrical resonance between the power supply and the ground surface.
In actual circuit boards, however, there are cases in which, for example, the conductor surface in the power supply layer is divided into a plurality by slits or the like in order to use plural voltages. In such a case, the configuration of the conductor surface grows complex, the resonance current is not distributed evenly in the power supply and ground surface, and the current is concentrated at a portion where the conductor width narrows, whereby the circuit board becomes a source for electromagnetic radiation. For this reason, there are instances in which the effect is small even when a technology that suppresses unwanted radiation by connecting a capacitor between the power supply and the ground surface at the circuit board end is applied.
In order to solve this problem, JP-A No. 11-54860 discloses a technology in which, as illustrated in FIG. 12, terminal loads 102 are connected to a power supply/ground surface at peripheral edges of an inner power supply surface 101 when a power supply layer surface 100 is divided into two power supply surfaces.
Further, JP-A No. 9-283974 discloses a technology in which, as illustrated in FIG. 13, with respect to an all-over power supply surface or a plurally-divided power supply surface of a power supply layer 112 of a printed circuit board 111, in order to suppress unwanted radiation resulting from fluctuations in electric potential between the power supply layer 112 and a ground layer 113, another ground layer 114 is disposed opposite the ground layer 113 with the power supply layer 112 interposed therebetween, and in which resistors 117 are connected between the two ground layers, to thereby form an RC parallel circuit of the capacity constituents due to a dielectric 116 present between the power supply and ground layer and the resistors 117, whereby fluctuations in electric potential are absorbed.
In this case, it is preferable for the capacity resulting from the dielectric 116 present between the power supply/ground layer to be large in order to absorb more fluctuations in electric potential. Particularly, in the conventional art above, capacitors 118 and 119 are connected between the power supply/ground layer at each divided layer to increase capacity constituents between the layers when the power supply surface is divided into a plurality of power supply surfaces, because the power supply layer area is small and it is difficult to alter the material of the dielectric for each divided power supply surface.
However, in the technology disclosed in JP-A No. 11-54860, as illustrated in FIG. 12, the terminal loads 102 must be connected between the power supply and ground surface across the entire peripheral edge of the divided power supply surface 101. Thus, there has been the problem that the number of terminal loads 102 rises which takes up space on the board for connecting the terminal loads 102.
Further, in the technology disclosed in JP-A No. 9-283974, as illustrated in FIG. 13, two ground layers 113 and 114 are required to suppress unwanted radiation between the power supply layer and ground layer, and space for connecting resistors 117 between ground layer 113 and the ground layer 114 becomes necessary. Further, capacitors 118 for increasing capacity constituents between the power supply layer 112 and the ground layer 114 increase as the power supply pattern configuration increases in complexity.